my $test = q{asdfas dfas dfas df asfd[[bad tag]] [[table]] asdfa sf as [[asdf as f\|sfds]] as dfa 
sdf [[test new line]] foo};

while ($test =~ m{\[\[([^\[]+)\]\]}g) {
  print "FOO:<$1>\n";
}

#output - same as required in OP
FOO:<bad tag>
FOO:<table>
FOO:<asdf as f\|sfds>
FOO:<test new line>